1. Field of the Invention
This invention pertains generally to circuit interrupters and, more particularly, to such circuit interrupters employing a processor. The invention also relates to methods for reducing current consumption for a circuit interrupter.
2. Background Information
Circuit interrupters include, for example, circuit breakers, contactors, motor starters, motor controllers, other load controllers and receptacles having a trip mechanism. Circuit breakers are generally old and well known in the art. Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which is heated and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system. An armature, which is attracted by the sizable magnetic forces generated by a short circuit or fault, also unlatches, or trips, the operating mechanism.
With the increasing popularity of portable battery-powered electronic devices (e.g., cell phones; MP3 players; digital cameras), many electronic manufacturers are developing components with features specifically designed for low-power operation. There are also many well-known design techniques for reducing the power consumed by microcontrollers including, for example, reducing power supply voltage, employing “sleep” modes (which reduce power supply current consumption by temporarily shutting off the microprocessor primary clock source) and employing relatively lower clock speeds. Of these techniques, it is believed that “sleep” modes cannot be used in a circuit breaker application, because too many cycles (and too much time) are required for the primary clock source to restart when the microprocessor “wakes up”. Also, it is believed that power supply voltage(s) and a single processor clock speed are selected to give the “best” overall performance in terms of desired processing capability and power consumption.
At least one manufacturer has introduced microcontrollers with a hardware feature that allows software selection between several internal clock frequencies. For instance, the Microchip PIC16F685 microcontroller, marketed by Microchip Technology Incorporated of Chandler, Ariz., has a 31 kHz internal clock and an 8 MHz internal clock with a postscaler. With the proper configuration, this microcontroller can be driven by an internal clock frequency of 31 kHz, 125 kHz, 250 kHz, 500 kHz, 1 MHz, 2 MHz, 4 MHz or 8 MHz. The microcontroller can switch between any of these internal clock frequencies while being operated by software control within a single microcontroller execution cycle.
The power supply of, for example, a microcomputer-based miniature circuit interrupter contributes to increases in internal operating temperature and, thus, may impact the normal operating temperature range of the circuit interrupter.
Accordingly, there is room for improvement in circuit interrupters.
There is also room for improvement in the current consumption of a circuit interrupter processor.